There is known an antenna component that is three-dimensionally designed by having an antenna element mounted on a surface of a dielectric substrate. The antenna component is mounted directly on a case of compact wireless communication device, such as a cellular phone, or on a circuit board, and is used as a built-in antenna. The antenna component is often called molded interconnect device (MID) antenna from its structural configuration.
The MID antenna is configured by providing an antenna as a compact modular component to be installed in a wireless communication device in the same manner as with other general components. However, limitations are imposed on a resin in terms of characteristics such as whether or not the resin can be subjected to dual molding, and whether or not the resin can be easily plated. The MID antenna uses a resin that is deficient in strength and undesirable for use as a case of a slim-type wireless communication device. Accordingly, the MID antenna is provided as a component separate from the case of the wireless communication device. Therefore, in order to simplify processes by means of further reducing the number of components, forming an antenna element on the surface (an interior surface or an exterior surface) of a case of the wireless communication device in place of use of the MID antenna is desirable. In general, when mounted on the wireless communication device, the antenna requires to be fine-adjusted due to the unignorable influence of metallic components disposed around the antenna. When an antenna is formed by use of a metal mold as in the case of the MID antenna, a long period is required for fine adjustment. Moreover, a plurality of metal molds may be required for performing the fine adjustment, and there is also a problem of consumption of a considerable initial investment before starting mass production of the antenna.
Conventionally, there is known a technique for forming conductor pattern in a portion of a case of a wireless communication device, connecting to a feeding point, and operating the pattern as an antenna. An example of such technique is disclosed in JP-A-2005-295578.
The document JP-A-2005-295578 discloses a techniques for configuring a built-in antenna, which to form one of cases of a clamshell cellular phone with a conductive material or to form the one of the cases with an insulating material and providing a conductor layer on the surface of the case; and connecting the case to a feeding point by being interposed therebetween with a conductive member that is included in a hinge mechanism. According to this configuration, the case of the cellular phone serves as a portion of the antenna.
Among the techniques disclosed in the document JP-A-2005-295578, the technique for forming the conductor layer for an antenna element on the surface of the case formed from an insulating material is more advantageous in terms of manufacturing cost than the technique of forming the case from a conductive material. However, the document JP-A-2005-295578 fails to disclose specifics about how to form the antenna element on the surface of the case made of an insulating material and how to ensure an antenna characteristic.